A power transmitting device (a charging platform) which wirelessly supplies electric power to a power receiving device by using electromagnetic induction is known. Examples of the power receiving device include a mobile phone. A user can charge a built-in battery of the power receiving device by wirelessly transmitted power only when placing the power receiving device on the power transmitting device. The power transmitting device is connected to a commercial power supply at all times so that the power receiving device can be charged at any time when the power receiving device is placed on the power transmitting device.
For the purpose of reducing power consumption, the power transmitting device transmits charging power when the power receiving device is located nearby and the power transmitting device does not transmit charging power when the power receiving device is not located nearby. For this purpose, for example, the power transmitting device transmits a PING signal at a certain time interval and checks whether or not the power receiving device is located nearby by the presence or absence of a response from the power receiving device. Therefore, the power transmitting device requires standby power of several mW to check the presence of the power receiving device even in a standby state where the power receiving device is not located nearby.